In this input end “windSpeed_tenMeters_”,whether the bigger the number of wind speed in summer,the more comfotable the environment. If it is not,what the mechanism of the “ladaybug outdoor comfortable calculator” is.I hope some can help me ,Thanks!
Wind speed is one of the inputs to calculate UTCI. You can read more about UTCI at www.utci.org as suggested in the component description.
NOTE: I’m not sure if you are suggesting that the results doesn’t change with changing the input values or are you asking about the basis of the calculation. I assumed it’s the second one. If it is the first one then you should provide your input and output values so we can help you with your question.
Outdoor thermal comfort is a complex phenomena. In addition to the website @mostapha mentioned, I would also recommend checking this paper.
How does the air movement really help?
It helps with convection and therefore helps with evaporating sweat from the skin. This effect is called “physiological cooling.”
So yes, to a certain extent wind of tolerable speeds will help. I say that because excessive wind speeds are not well received in public realms. Please look for the Beaufort Scale and the Lawson’s criteria on pedestrian comfort to know more about the effects of excessive wind speeds on outdoor human comfort.
Also, please note that when you use wind velocity from the weather data, the UTCI you get is a city level UTCI. It is UTCI that someone who is walking at the speed of 4 km/h in an open farm can experience. In order to calculate site specific UTCI, CFD simulations are required.
Lastly, it has been observed in many sensitvity analysis studies of UTCI that the incident solar radiation is the variable that has the biggest impact on UTCI.
@devang my understanding of the Beaufort Scale is that it measures pedestrian comfort in terms of pedestrian safety, and not thermal comfort. Can you find any references that help translate the Beaufort index to cooling effect?
The Lawson Comfort Criteria is more relevant because it defines a range of suitable wind conditions in an urban environment based on speed and duration. The Lawson Comfort Criteria assumes that humans compensate for thermal discomfort with changes to clothing and people will be appropriately dressed for the weather conditions. It should be noted that the Lawson Comfort Criteria was designed based on research in cold climates and does not reflect the desired wind speeds in hot conditions, when air movement can add a cooling effect (3).
(2) T.V. Lawson, Building Aerodynamics (Imperial College Press, April 2001), 125-135.
(3) Task Committee on Outdoor Human Comfort of the Aerodynamic Committee of the American Society of Civil Engineer (ASCE). Outdoor Human Comfort and It’s Assessment . (American Society of Civil Engineers, 2003).
The UTCI calculation was derived from studying individuals while walking (135 W/m2). I’ve interpreted this as the UTCI metric only being directly appropriate for individuals at the same metabolic rate. Have you seen any attempts to convert the UTCI temperatures for a sedentary person?
Hi @KitElsworth
I have not come across any reference that pedestrian safety and thermal comfort.
In hot & humid climates, designers have a tendency to expect / achieve high wind velocities to influence the thermal comfort. I believe that pedestrian comfort shall also be monitored in presence of such tendencies therefore I recommended here.
One of the assumption of the reference condition for UTCI is indeed that a human is walking at the speed of 4km/h at the metabolic rate of 135 w/m2. I was aware of that. Thanks for pointing that out. It was lazy of me to mention that “it is UTCI someone who is standing in an open farm can experience.” I will edit that statement.
I didnt mean to point out any laziness! I simply wanted to jump at the opportunity to see if anyone has been able to utilize UTCI for sedentary activity. This has been a topic of interest for me but a topic that has been on the “back-burner” for quite some time now. Thanks for the extra insight @devang